The present invention relates generally to radome structures or the like typically disposed external of an aircraft that are vulnerable to out of plane loadings, and more particularly to an elastically collapsible, impact resistant sandwich structure for radomes, de-icer elements or the like.
Radome structures are typically mounted to the nose of an aircraft and are therefore subject to bird strikes in flight. Existing radome structures comprise an astroquartz epoxy structure with layered flute and skin sub-structures, designed primarily for radar performance, with the open flute structures carrying hot air near the outer surface for de-icing purposes. The structure is made by bonding a lower structure to a top-hat-shaped skin and then bonding this intermediate structure to a top skin. This structure undergoes crushing of the open cells when impacted by relatively small objects such as birds in flight. The damage has been considered unavoidable and the structure subsequently repaired or replaced. Electronic performance considerations require that in high-performance radar systems that use de-icing technology energy absorption be accomplished without changing the material or the overall thickness of the structure.
The invention solves or substantially reduces in critical importance problems with prior art structures as just described by providing an elastically collapsible open-celled sandwich structure for radome or similar structures that can absorb without damage the impact of out-of-plane loadings such as bird strikes. The structure of the invention eliminates bonding between the open cells and the outer and central skins to facilitate elastic collapse and includes sine-wave shaped cells to eliminate stress concentrations. During impact, the open cells move independently of the constraining skins, collapse and return to the original shape without permanent structural damage. The invention may be used in substantially any sandwich structure requiring impact resistance.
It is therefore a principal object of the invention to provide an impact resistant, elastically collapsible, open celled sandwich structure.
It is another object of the invention to provide improved radome, de-icer or other like structures for aircraft.
It is a further object of the invention to provide radome, de-icer or similar structures having improved resistance to out-of-plane loadings such as bird strikes.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.
In accordance with the foregoing principles and objects of the invention, an impact resistant structure is described that includes a substantially sinusoidally shaped elastically collapsible open-celled fluted layer disposed between but not bonded to constraining layers, whereby in an impact event, the flutes are free to move between the constraining layers and stress concentrations in the collapsing flutes immediately beneath the impacting object are minimized by the absorption of impact forces by neighboring flutes that resiliently collapse in an accordion-like fashion, and return substantially to the original shape after impact without permanent damage to the structure.